Aerospace and Electronic Systems Magazine September 2016 - 55

Kotegawa

Figure 2.

ACAS-XU equipment onboard NASA Ikhana.

scenarios were tuned for the quantitative well clear definition mentioned above.

SELF-SEPARATION: AIRBORNE SENSORS WITH SAA
DISPLAYS IN GCS
The objective of SS is to remain "well clear" of nearby air traffic
and prevent progression to a collision avoidance situation. The current FAA definition for UAS well clear is to maintain a minimum τ
(estimated time to CPA) of 35 s from any airborne threats. The well
clear definition also includes a distance modification (DMOD) to
maintain distance of at least 4000 ft horizontally and 700 ft vertically from threats regardless of τ, to protect from slow closure rate
encounters [5].
The remote pilot needs to understand the potential conflict
that can arise from nearby threats in case air traffic control
(ATC) or the intruder do not resolve it in time, and perform the
minimal maneuvers to prevent the projected well clear violation. Projection and assessment of air traffic to maintain well
clear requires significant mental workload on the pilot. The SS
display reduces this mental workload by providing the pilot current and projected situational awareness in an intuitive manner
as well as recommend actions to avoid upcoming conflicts. The
SS encounter scenarios were similar to the CA runs, but it was
up to the remote pilot to determine when and how much of the
recommended maneuver from the SS to execute. For example,
if an SS display recommended a 20 deg heading change, conservative pilots may maneuver immediately as well as add buffer
and less conservative pilots may wait to react until the situation
becomes more urgent.
The flight tests examined three prototype SS displays developed by GA-ASI and NASA. Data collection for the SS scenarios
centered on how well the pilot interfaced with the displays, and
its overall ability for the UAS to remain well clear (e.g., pilot reaction times, intuitiveness, number and seriousness of well clear
violations, etc.). However, at the time of the flight test, the well
clear standard was not yet defined and not all displays/encounter
SEPTEMBER 2016

TEST PLATFORM SUMMARY
TEST AIRCRAFT - NASA 870 "IKHANA"
NASA provided their unmanned research aircraft "Ikhana" (variant of the GA-ASI Predator B) (see Figure 2) as the primary test
aircraft. Ikhana was equipped with additional avionics to enable
SAA functionality, including the Honeywell TPA-100A TCAS II
unit, BAE AN/DPX-7 Reduced-size Transponder with ADS-B
1090 ES IN/OUT, GA-ASI Due Regard Radar (DRR), and Sense
and Avoid Processor (SAAP) hosting the ACAS XU software. The
TCAS II and DPX-7 are certified units under the FAA Technical
Standard Orders (TSO), while the SAAP and DRR are units under
test during this flight test. In the GCS, three SAA displays were
installed: Conflict Prediction and Display System (CPDS) developed by GA-ASI, and StratWay+ and Autoresolver both developed
by NASA. Traffic information was shared from Ikhana to the SAA
displays through NASA's Live Virtual Constructive Distributed
Environment (LVC-DE), which also allowed researchers to observe the tests remotely. Modification on legacy GCS and flight
control software further enabled automatic maneuvers from the
ACAS XU RAs and appropriate interface with the pilot station.

INTRUDER AIRCRAFT
Three manned intruders provided by FAA, Honeywell, and NASA
flew on encounters against Ikhana. Each intruder aircraft with its
unique flight characteristic, size (for radar), and onboard surveillance equipment (TCAS I, TCAS II, ADS-B, GPS recorder, etc.)
contributed to demonstrate the various aspects of ACAS XU functionality such as interoperability with TCAS and interoperability

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Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine September 2016